The ability to sustain conventional agriculture is based upon a high input of agrochemicals, such as phosphate-containing fertilizers. Conventional inorganic phosphorous fertilizers may cause an inadvertent addition of heavy metals, which are contained as impurities.
For example, an analysis of phosphate fertilizers commonly used in Argentina was performed to determine the concentrations of heavy metals (such as chromium, cadmium, copper, zinc, nickel, and lead) found therein. L. Guiffre de Lopez Camelo et al., “Heavy Metals Input with Phosphate Fertilizers used in Argentina,” Sci. Total Environ., 204(3): 245–250 (1997). The analysis revealed that: rock phosphate fertilizers contain the highest levels of cadmium and zinc; diammonium phosphate fertilizers contain enhanced levels of chromium; while superphosphate fertilizers contain the highest levels of copper and lead. Id. Thus, the continuous fertilization of soils could increase the heavy metal contents exceeding natural abundances in soils, and result in the transfer of these metals to the human food chain. Id.
Moreover, agricultural phosphate overfertilization creates environmental problems (e.g. contamination of water) and will lead to a depletion of naturally occurring phosphate fertilizer resources in the near future. Therefore, it is highly desirable to develop new strategies to reduce the amount of phosphate fertilizer needed for the optimal growth of crop plants.